Illuminating lens, and lighting device

ABSTRACT

An illuminating lens includes: a light entrance surface through which light emitted from a light source enters the lens; and a light exit surface through which the light that has entered the lens exits the lens. The light exit surface has: a concave portion intersecting the optical axis; and a convex portion provided around the concave portion to extend continuously from the concave portion. The light exit surface is formed in a shape such that a curvature C of micro-segments of the light exit surface in a cross section including the optical axis has a maximum value at a position outward from the midpoint of the convex portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 12/752,722,filed Apr. 1, 2010, which is a Continuation of PCT/JP2009/003556, filedJul. 28, 2009, which applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illuminating lens for widening arange of transmission directions for light from a light source such as alight emitting diode, and to a lighting device using this illuminatinglens. The present invention further relates to a surface light sourceincluding a plurality of lighting devices, and to a liquid-crystaldisplay apparatus in which this surface light source is disposed behinda liquid-crystal panel to serve as a backlight.

2. Description of Related Art

In a conventional backlight of a large-sized liquid-crystal displayapparatus, a number of cold cathode tubes are disposed immediately belowa liquid-crystal panel, and these cold cathode tubes are used with othermembers such as a diffusing plate and a reflecting plate. In recentyears, light emitting diodes have been used as light sources forbacklights. Light emitting diodes have increased their efficiencyrecently, and are expected to serve as low-power light sources toreplace fluorescent lamps. In the case where light emitting diodes areused as a light source in a liquid-crystal display apparatus, the powerconsumption of the apparatus can be reduced by controlling the light anddark states of the light emitting diodes according to an image to bedisplayed.

In a backlight of a liquid-crystal display apparatus using lightemitting diodes as a light source, a large number of light emittingdiodes are disposed therein instead of cold cathode tubes. The use of alarge number of light emitting diodes allows the entire surface of thebacklight to have uniform brightness, but the need for such a largenumber of light emitting diodes is an obstacle to cost reduction. Inview of this, attempts to increase the output power of each lightemitting diode to reduce the required number of light emitting diodeshave been made. For example, Japanese Patent No. 3875247 has proposed alens that is designed to provide a uniform surface light source with areduced number of light emitting diodes.

In order to obtain a uniform surface light source with a reduced numberof light emitting diodes, the area to be irradiated with the lightemitted from each light emitting diode needs to be increased. That is,light emitted from each light emitting diode needs to be spread toobtain a wider range of transmission directions for light from thediode. For this purpose, in Japanese Patent No. 3875247, a lens having acircular shape in a plan view is disposed on a light emitting diode as achip to control the directivity of the chip. The light exit surface ofthis lens, through which light exits the lens, has a shape such that aportion in the vicinity of the optical axis is a concave and a portionsurrounding the concave is a convex extending continuously from theconcave.

A light emitting diode as a chip emits light mostly in the frontdirection of the light emitting diode chip. In the lens disclosed inJapanese Patent No. 3875247, light that has been emitted in the frontdirection of the chip is diffused on the concave surface in the vicinityof the optical axis.

In the lens disclosed in Japanese Patent No. 3875247, the curvatureradius of the light exit surface in a cross section including theoptical axis has the smallest value at a position on the convex adjacentto the concave, and the portion outward from the vertex of the convex isan approximately conical surface. With the light exit surface havingsuch a shape, however, there is a limit to a widening of the range oftransmission directions for light from the light source.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an illuminating lenscapable of further widening the range of transmission directions forlight from a light source, and to provide a lighting device, a surfacelight source, and a liquid-crystal display apparatus each including thisilluminating lens.

In order to achieve the above object, an illuminating lens according tothe present invention is an illuminating lens for spreading lightemitted from a light source so that a surface to be irradiated isirradiated with the spread light, and is characterized as follows. Theilluminating lens includes: a light entrance surface through which thelight emitted from the light source enters the lens; and a light exitsurface through which the light that has entered the lens exits thelens, the light exit surface being rotationally symmetric with respectto an optical axis. In this illuminating lens, the light exit surfacehas a concave portion and a convex portion. The concave portionintersects the optical axis, and the convex portion is provided aroundthe concave portion to extend continuously from the concave portion. Thelight exit surface is formed in a shape such that a curvature C ofmicro-segments of the light exit surface in a cross section includingthe optical axis has a maximum value at a position outward from amidpoint of the convex portion.

The sign of the curvature C is positive if the center of the curvatureis located on the light source side of the light exit surface, andnegative if the center of the curvature is located on the side oppositeto the light source.

In such a configuration, light emitted from the light source can reach alarger area on the surface to be irradiated, and thus the resultingilluminating lens can widen the range of transmission directions forlight from the light source further than before.

A lighting device according to the present invention is characterized inthat it includes: a light emitting diode for emitting light; and theabove-mentioned illuminating lens for spreading light emitted from thelight emitting diode so that a surface to be irradiated is irradiatedwith the spread light.

With such a configuration, the lighting device having a wide range oftransmission directions of light can be obtained.

A surface light source according to the present invention ischaracterized in that it includes: a plurality of lighting devicesarranged in a plane; and a diffusing plate disposed to cover theplurality of lighting devices, and configured to receive on one surfacethereof light emitted from the plurality of lighting devices and to emitthe light from the other surface thereof in a diffused manner. Each ofthe plurality of lighting devices is the above-mentioned lightingdevice.

With such a configuration, the surface light source having less unevenbrightness in the plane can be obtained.

A liquid-crystal display apparatus according to the present invention ischaracterized in that it includes: the above-mentioned surface lightsource; and a liquid-crystal panel that is to be irradiated with lightemitted from the surface light source disposed behind the liquid-crystalpanel.

With such a configuration, the liquid-crystal display apparatus havingless uneven brightness can be obtained.

According to the present invention, the range of transmission directionsfor light from the light source can be widened even further than before.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illuminating lens according to afirst embodiment of the present invention.

FIG. 2 is a schematic diagram of a lighting device according to a secondembodiment of the present invention.

FIG. 3 is a diagram showing optical paths of light rays emitted from thelighting device according to the second embodiment of the presentinvention.

FIG. 4 is a diagram for explaining a curvature C of micro-segments on alight exist surface and θi indicating the position of one of themicro-segments.

FIG. 5A is a diagram for explaining a method of deriving a curvature Cof micro-segments, and FIG. 5B is an enlarged view of one of themicro-segments.

FIG. 6 is a diagram for explaining parameters of an inequality (4).

FIG. 7 is a schematic diagram of a modified illuminating lens.

FIG. 8 shows an illuminance distribution obtained by using anilluminating lens of Example 1 in a lighting device.

FIG. 9 shows an illuminance distribution obtained by using only lightemitting diodes to confirm the effect of the illuminating lens ofExample 1.

FIG. 10 is a diagram showing a relationship between θi and a curvature Cof micro-segments of the illuminating lens of Example 1.

FIG. 11 is a diagram showing a relationship between θi and C×(n−1)×di ofthe illuminating lens of Example 1.

FIG. 12 is a diagram showing a relationship between θi, and a curvatureC of micro-segments and a sag amount of the illuminating lens of Example1.

FIG. 13 is a diagram showing a relationship between θi and Δθr/Δθi ofthe illuminating lens of Example 1.

FIG. 14 shows a luminous intensity distribution of light emitted fromthe light exit surface of the illuminating lens of Example 1.

FIG. 15 shows an illuminance distribution obtained by using anilluminating lens of Example 2 in a lighting device.

FIG. 16 shows an illuminance distribution obtained by using only lightemitting diodes to confirm the effect of the illuminating lens ofExample 2.

FIG. 17 is a diagram showing a relationship between θi and a curvature Cof micro-segments of the illuminating lens of Example 2.

FIG. 18 is a diagram showing a relationship between θi and C×(n−1)×di ofthe illuminating lens of Example 2.

FIG. 19 is a diagram showing a relationship between θi, and a curvatureC of micro-segments and a sag amount of the illuminating lens of Example2.

FIG. 20 is a diagram showing a relationship between θi and Δθr/Δθi ofthe illuminating lens of Example 2.

FIG. 21 shows a luminous intensity distribution of light emitted fromthe light exit surface of the illuminating lens of Example 2.

FIG. 22 shows an illuminance distribution obtained by using anilluminating lens of Example 3 in a lighting device.

FIG. 23 shows an illuminance distribution obtained by using only lightemitting diodes to confirm the effect of the illuminating lens ofExample 3.

FIG. 24 is a diagram showing a relationship between θi and a curvature Cof micro-segments of the illuminating lens of Example 3.

FIG. 25 is a diagram showing a relationship between θi and C×(n−1)×di ofthe illuminating lens of Example 3.

FIG. 26 is a diagram showing a relationship between θi, and a curvatureC of micro-segments and a sag amount of the illuminating lens of Example3.

FIG. 27 is a diagram showing a relationship between θi and Δθr/Δθi ofthe illuminating lens of Example 3.

FIG. 28 shows a luminous intensity distribution of light emitted fromthe light exit surface of the illuminating lens of Example 3.

FIG. 29 is a schematic diagram of a surface light source according to athird embodiment of the present invention.

FIG. 30 is a partial cross-sectional view of the surface light sourceaccording to the third embodiment of the present invention.

FIG. 31 is a plan view showing another arrangement of lighting devices.

FIG. 32 is a schematic diagram of a liquid-crystal display apparatusaccording to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

An illuminating lens according to the first embodiment of the presentinvention will be described with reference to the accompanying drawings.FIG. 1 is a schematic diagram of an illuminating lens 100 according tothe first embodiment. The illuminating lens 100, which is disposedbetween a light source (not shown in FIG. 1) having directivity and asurface to be irradiated 300, spreads light emitted from the lightsource and emits the spread light to the surface to be irradiated 300.That is, the illuminating lens 100 widens the range of transmissiondirections for light from the light source. In the illuminancedistribution on the surface to be irradiated 300, the illuminance isgreatest on the optical axis A that is the design center line of theilluminating lens 100 and decreases almost monotonically toward theedge. The light source and the illuminating lens 100 are disposed sothat their optical axes coincide with each other.

Specifically, the illuminating lens 100 has a light entrance surface 111through which the light emitted from the light source enters the lensand a light exit surface 120 through which the light that has enteredthe lens exits the lens. The illuminating lens 100 has a bottom surface112 surrounding the light entrance surface 111 and facing oppositely tothe light exit surface 120. The illuminating lens 100 further has anouter peripheral surface 130 located outwardly of the light exit surface120 to connect the periphery of the light exit surface 120 and the outeredge of the bottom surface 112.

The light entrance surface 111 need not be rotationally symmetric withrespect to the optical axis. In the present embodiment, the lightentrance surface 111 is located closer to the light exit surface 120than the annular bottom surface 112 surrounding the light entrancesurface 111, and the light source is fitted in the recess formed by thelevel difference between the surfaces 111 and 112. The light entrancesurface 111 and the bottom surface 112 may be located on the same level.In this case, the light entrance surface 111 is the area that isconnected optically to the light source. The light entrance surface 111need not necessarily be joined directly to the light source. Forexample, the light entrance surface 111 may be recessed in ahemispherical shape so that an air space is formed between the lightentrance surface 111 and the light source.

The light exit surface 120 is rotationally symmetric with respect to theoptical axis. The light exit surface 120 is the area (area locatedinwardly of a point P shown in FIG. 1) for controlling at least aspecified amount (for example, 90%) of light emitted from the lightsource. The diameter of the light exit surface 120 is the effectivediameter De of the illuminating lens 100 when viewed from the opticalaxis direction.

The outer peripheral surface 130 forms a curved surface extendingcontinuously from the light exit surface 120 in the present embodiment,but may be a tapered surface having a linear cross section.Alternatively, the illuminating lens 100 may be provided with a ringportion 150 projecting from the entire periphery of the light exitsurface 120 so that the end surface of the ring portion 150 serves asthe outer peripheral surface 130, as shown in FIG. 7, for example. Theouter peripheral surface 130 need not be rotationally symmetric withrespect to the optical axis. For example, the outer peripheral surface130 may have a pair of flat portions that are parallel to each otheracross the optical axis such that the illuminating lens 100 has an ovalshape when viewed from the optical axis direction.

The light emitted from the light source enters the illuminating lens 100through the light entrance surface 111, exits the lens 100 through thelight exit surface 120, and then reaches the surface to be irradiated300. The light emitted from the light source is spread by the action ofthe light exit surface 120, and reaches a large area of the surface tobe irradiated 300.

As the light source, for example, a light emitting diode can be used.Light emitting diodes usually are chips with a rectangular plate shape.Therefore, it is preferable that the light entrance surface 111 of theilluminating lens 100 have a shape conforming to the shape of a lightemitting diode to fit in close contact with the light emitting diode.The light emitting diode is in contact with the light entrance surface111 of the illuminating lens 100 via a bonding agent, and connectedoptically to the light entrance surface 111. The light emitting diodeusually is covered with a sealing resin to avoid contact with air. As aconventional sealing resin for a light emitting diode, an epoxy resin,silicone rubber, or the like is used.

The illuminating lens 100 is made of a transparent material having aspecified refractive index. The refractive index of the transparentmaterial is, for example, about 1.4 to 1.53. Examples of such atransparent material include resins such as epoxy resin, silicone resin,acrylic resin, and polycarbonate, and rubbers such as silicone rubber.Particularly, it is preferable to use epoxy resin, silicone rubber, orthe like that has been used as a sealing resin for a light emittingdiode.

The light exit surface 120 includes a concave portion 121 intersectingthe optical axis and a convex portion 122 provided around the concaveportion 121 to extend continuously from the concave portion 121. Lightenters the illuminating lens 100 through the light entrance surface 111at a wide range of angles. Light that has entered the lens at a smallangle with respect to the optical axis reaches the concave portion 121,and light that has entered the lens at a larger angle with respect tothe optical axis reaches the convex portion 122.

For more detail, the light exit surface 120 is formed in a shape suchthat the curvature C of micro-segments of the light exit surface 120 ina cross section including the optical axis has a maximum value at aposition outward from the midpoint (point M indicated in FIG. 1) of theconvex portion 122.

The curvature C of the micro-segments is described below with referenceto FIG. 4 and FIGS. 5A and 5B. FIG. 4 shows the curvature C ofmicro-segments of the light exist surface 120 and an angle θi indicatingthe position of one of the micro-segments. The curvature C ofmicro-segments is defined as follows based on the position of the lightsource on the optical axis. The “position of the light source on theoptical axis” is a position at which the optical axis intersects thelight emitting surface of the light source.

As shown in FIGS. 5A and 5B, a micro-segment between a point A and apoint B on the light exit surface 120 is assumed to be an n-thmicro-segment from the optical axis. In this case, an angle between theoptical axis and a line connecting the point A and the position of thelight source on the optical axis is denoted as θi(n), and an anglebetween the optical axis and a line connecting the point B and theposition of the light source on the optical axis is denoted as θi(n+1),where θi(n+1)−θi(n) is about 0.5 degrees. An angle between a tangent atthe point A on the light exit surface 120 and a surface perpendicular tothe optical axis is denoted as θs(n), and an angle between a tangent atthe point B on the light exit surface 120 and a surface perpendicular tothe optical axis is denoted as θs(n+1). The length of a section betweenthe point A and the point B on the light exit surface 120 is denoted asΔd(n). Assuming that the A-B section of the light exit surface 120,which is assumed to be sufficiently small, is represented by a singlecurvature radius R, since the center O of the radius R is a point ofintersection of a normal at the point A on the light exit surface 120and a normal at the point B on the light exit surface 120, an angle ∠AOBbetween these two normals can be represented as θs(n+1)−θs(n). Theradius R of the arc between the point A and the point B with O being thecenter thereof can be represented as Δd(n)/θs(n+1)−θs(n). The curvatureC is 1/R. Accordingly, the curvature C of the n-th micro-segment isrepresented as (θs(n+1)−θs(n))/Δd(n). In this case, θs(n) and θs(n+1)are defined by the radian measure. In the above definitions, the sign ofthe curvature C is positive when the center of curvature O is located onthe light source side of the light exit surface 120, and negative whenthe center of curvature O is located on the opposite side.

According to the present embodiment, it is possible to obtain theilluminating lens 100 capable of emitting light that has entered thelens through the light entrance surface 111 through the light exitsurface 120 toward a larger area.

The object of the present invention is achieved by the above-mentionedconfiguration. It is more preferable, however, from a functionalviewpoint, that the illuminating lens 100 of the present embodimentsatisfies the following conditional items.

It is preferable that the curvature C of the micro-segments of the lightexit surface 120 in the cross section including the optical axis has themaximum value under the condition defined by the following inequality(1):

60°<θi<80°  (1)

(more preferably, 65°<θi<75°  (1)′)

where θi is the angle between the optical axis and the line Liconnecting the position of the light source on the optical axis and thecenter of each of the micro-segments, that is, θi≈(θi(n+1)+θi(n))/2 (seeFIG. 4).

The inequality (1) (or the inequality (1)′) defines the shape of thelight exit surface 120 based on the premise that a light ray emittedfrom the light source is incident at the position on the light exitsurface 120 in the direction of θi from the position of the lightsource.

If the value of θi exceeds the upper limit of the inequality (1) (or theinequality (1)′), closer tolerances are required to maintain the lightdistribution characteristic, which increases the unevenness of in-planebrightness in the case of a surface light source. If the value of θi isless than the lower limit, the light distribution characteristicdeteriorates, which increases the unevenness of in-plane brightness inthe case of a surface light source.

Alternatively, it is preferable that the curvature C of themicro-segments of the light exit surface in the cross section includingthe optical axis has the maximum value under the condition defined bythe following inequality (2):

0.88<Yr<0.98  (2)

(more preferably, 0.90<Yr<0.96  (2)′)

where Yr is the ratio of the distance Di from the optical axis to thecenter of each of the micro-segments with respect to half the effectivediameter De of the illuminating lens 100, that is, Di/0.5 De (see FIG.4).

The inequality (2) (or the inequality (2)′) defines the shape of thelight exit surface 120 based on the premise that a light ray emittedfrom the light source is incident at the position on the light exitsurface 120 with a ratio Yr.

If the value of Yr exceeds the upper limit of the inequality (2) (or theinequality (2)′), closer tolerances are required to maintain the lightdistribution characteristic, which increases the unevenness of in-planebrightness in the case of a surface light source. If the value of Yr isless than the lower limit, the light distribution characteristicdeteriorates, which increases the unevenness of in-plane brightness inthe case of a surface light source.

Furthermore, it is preferable that the light exit surface 120 satisfiesthe following inequality (3):

0.90<θmp/θmc<1.05  (3)

(more preferably, 0.92<θmp/θmc<1.03  (3)′)

where θmc is the angle between the optical axis and the line Lconnecting the position of the light source on the optical axis and thecenter of a micro-segment in which the curvature C has a maximum valueamong the micro-segments, and θmp is, among emission angles that areangles between light rays emitted from the light exit surface 120 andthe optical axis, the emission angle having a maximum luminousintensity, where the light rays are sorted by respective emission angles(see FIG. 6).

The inequality (3) (or the inequality (3)′) defines the ratio betweenθmp and θmc. If the value of θmp/θmc exceeds the upper limit of theinequality (3) (or the inequality (3)′), the angle of θmp is excessivelylarge with respect to the angle θmc, which causes a decrease in thelight emission intensity, and thus the light distribution characteristicdeteriorates. If the value of θmp/θmc is less than the lower limit, thelight distribution characteristic varies in a wave-like manner, whichcauses uneven brightness.

Furthermore, it is preferable that the light exit surface satisfies thefollowing inequality (4):

0.9<Cm×(n−1)×d<1.5  (4)

(more preferably, 0.95<Cm×(n−1)×d<1.45  (4)′)

where Cm is the maximum value of the curvature C of the micro-segments,n is the refractive index of the illuminating lens 100, and d is thedistance from the position of the light source on the optical axis tothe center of a micro-segment in which the curvature C has a maximumvalue among the micro-segments, that is, the length of the line L (seeFIG. 6).

In the inequality (4) (or the inequality (4)′), the maximum value of thecurvature is normalized with respect to the distance from the positionof the light source to the light exit surface 120 to define the shape ofthe light exit surface 120. If the value of Cm×(n−1)×d exceeds the upperlimit of the inequality (4) (or the inequality (4)′), the light emissionintensity decreases at an angle at which the light emission intensityhas a maximum value. If the value of Cm×(n−1)×d is less than the lowerlimit, the light emission intensity decreases at an angle at which thelight emission intensity has a maximum value.

Furthermore, it is preferable that if a sag amount of the light exitsurface 120 is a height from a position where the light exit surface 120intersects the optical axis, the light exit surface 120 satisfies thefollowing inequalities (5) and (6):

5°<θo<20°  (5): and

25°<θs<45°  (6)

(more preferably, 10°<θo<15°  (5)′: and

30°<θs<40°  (6)′)

where θo is the angle between the optical axis and the line connectingthe position of the light source on the optical axis and the position atwhich the sign of the curvature C on the light exit surface 120 changesfrom negative to positive, and θs is the angle between the optical axisand the line connecting the position of the light source on the opticalaxis and the position at which the sag amount on the light exit surfacehas a maximum value.

The sign of the curvature C is positive when the light exit surface 120is located on the side opposite to the light source, and negative whenthe surface 120 is located on the light source side, with respect to thepoint of intersection of the optical axis and the light exit surface120.

The inequality (5) (or the inequality (5)′) and the inequality (6) (orthe inequality (6)′) define the shape of the light exit surface 120.

If the value of θo exceeds the upper limit of the inequality (5) (or theinequality (5)′), the incident angle of the light ray on the light exitsurface 120 is excessively large, and is totally reflected. As a result,a desired brightness distribution cannot be obtained, which increasesthe unevenness of in-plane brightness in the case of a surface lightsource. If the value of θo is less than the lower limit, the amount ofthe light ray directed to the center of the surface to be irradiated 300is high, which increases the unevenness of in-plane brightness in thecase of a surface light source. If the value of θs exceeds the upperlimit of the inequality (6) (or the inequality (6)′), closer tolerancesare required to maintain the light distribution characteristic. If thevalue of θs is less than the lower limit, the light distributioncharacteristic deteriorates, which increases the unevenness of in-planebrightness in the case of a surface light source.

Furthermore, it is preferable that the light exit surface 120 is formedas a continuous surface except for a point on the optical axis. The areanear the optical axis of the concave portion 121 on the light exitsurface 120 may be recessed toward a point on the optical axis. The areaalso may be curved smoothly to cross the optical axis at right angles.

With such a configuration, a smooth brightness distribution can beobtained in the case of a surface light source, and thus the unevennessof brightness can be reduced.

Furthermore, it is preferable that the illuminating lens 100 satisfiesthe following inequality (7):

1.40<n<1.52  (7)

where n is the refractive index of the illuminating lens 100.

The inequality (7) defines the refractive index of the illuminatinglens.

If the value of n exceeds the upper limit of the inequality (7), therefraction effect of the light exit surface 120 increases, which causesan insufficient light distribution characteristic. If the value of n isless than the lower limit, the refraction effect of the light exitsurface 120 decreases. Therefore, if the shape of the light exit surface120 is changed to increase the refraction effect, closer tolerances arerequired.

Furthermore, as shown in FIG. 3, it is preferable that in the case wherea light ray emitted from the position of the light source on the opticalaxis at an angle of θi with respect to the optical axis is refracted atthe light exit surface 120 at an angle of θr with respect to the opticalaxis, a variation Δθr in the angle θr with respect to an increment Δθiin the angle θi (Δθr/Δθi) with an increase in the angle θi increases anddecreases repeatedly.

Since the light source has a light emitting surface of a certain size,light emitted from the peripheral portion of the light emitting surfaceis totally reflected at the light exit surface 120. In the illuminancedistribution, the illuminance decreases locally due to this totalreflection of light. However, light rays can be guided to the lowilluminance region by designing the lens to satisfy the above conditionof Δθr/Δθi and to adjust the density of light rays. As a result, asmooth illuminance distribution can be obtained.

Second Embodiment

FIG. 2 is a schematic diagram of a lighting device 700 according to asecond embodiment of the present invention. This lighting device 700includes a light emitting diode 200 for emitting light, and theilluminating lens 100 described in the first embodiment for spreadinglight emitted from the light emitting diode 200 so that the surface tobe irradiated 300 is irradiated with the spread light.

The light emitting diode 200 is in contact with the light entrancesurface 111 of the illuminating lens 100 via a bonding agent, andconnected optically to the light entrance surface 111. The light thathas exited the illuminating lens 100 through the light exit surface 120reaches the surface to be irradiated 300, and thus the surface to beirradiated 300 is illuminated with that light.

Light generation in the light emitting diode 200 has no directivity initself, and a light emitting region has a refractive index of at least2.0. When light from the light emitting region enters a low refractiveregion, the refraction of the light at the interface causes the light tohave the maximum intensity in the normal direction of the interface andto have a lower intensity as the angle of the light with respect to thenormal increases. As described above, since the light emitting diode 200has high directivity, it is necessary to widen the range of transmissiondirections for light therefrom using the illuminating lens 100 toilluminate a larger area.

FIG. 3 is a diagram showing the paths of light rays in the lightingdevice 700. The light that has been emitted from the light emittingdiode 200 passes through the light entrance surface 111 and reaches thelight exit surface 120. The light that has reached the light exitsurface 120 passes through the light exit surface 120 while beingrefracted, and then reaches the surface to be irradiated 300.

It is preferable that the lighting device 700 satisfies the followinginequality (8):

0.3<D/t<0.9  (8)

(more preferably, 0.37<D/t<0.87  (8)′)

where D is the maximum width of the light emitting surface of the lightemitting diode 200 (the length of each side of the light emittingsurface if it is a square, and the length of the longer side of thelight emitting surface if it is a rectangle), and t is the centerthickness of the illuminating lens 100 (the distance from the lightentrance surface 111 to the light exit surface 120 on the optical axis)(see FIG. 3 and FIG. 4).

The inequality (8) (or the inequality (8)′) defines the maximum width ofthe light emitting surface of the light emitting diode 200 with respectto the center thickness of the illuminating lens 100.

If the value of D/t exceeds the upper limit of the inequality (8) (orthe inequality (8)′), the size of the light emitting diode 200 isexcessively large with respect to the size of the illuminating lens 100.Therefore, light rays directed to the light exit surface 120 areincident on the surface 120 at large angles, and are totally reflected.As a result, a desired brightness distribution cannot be obtained, whichincreases the unevenness of in-plane brightness in the case of a surfacelight source. If the value of D/t is less than the lower limit, the sizeof the illuminating lens 100 is excessively large with respect to thesize of the light emitting diode 200. Therefore, the lighting deviceincreases in size, which causes an increase in cost.

Furthermore, it is preferable that the lighting device 700 satisfies thefollowing inequality (9):

0.06<D/De<0.27  (9)

(more preferably, 0.09<D/De<0.24  (9)′)

where D is the maximum width of the light emitting surface of the lightemitting diode 200, and De is the effective diameter of the illuminatinglens 100.

The inequality (9) (or the inequality (9)′) defines the maximum width ofthe light emitting surface of the light emitting diode 200 with respectto the effective diameter of the illuminating lens 100. If the value ofD/De exceeds the upper limit of the inequality (9) (or the inequality(9)′), the size of the light emitting diode 200 is excessively largewith respect to the effective diameter of the illuminating lens 100.Therefore, light rays directed to the light exit surface 120 areincident on the surface 120 at large angles, and are totally reflected.As a result, a desired brightness distribution cannot be obtained, whichincreases the unevenness of in-plane brightness in the case of a surfacelight source. If the value of D/De is less than the lower limit, theeffective diameter of the illuminating lens 100 is excessively largewith respect to the size of the light emitting diode 200. Therefore, thelighting device increases in size, which causes an increase in cost.

EXAMPLES

Hereinafter, Examples 1 to 3 are given as specific numerical examples ofthe illuminating lens 100 used in the lighting device 700 according tothe second embodiment.

In each of the following examples, the units of lengths are allmillimeters (mm), and the units of angles are all degrees (°) in Tablesbelow. In the surface data in each of the following examples, r is acurvature radius, d is a distance between surfaces or a thickness of alens, and n is a refractive index with respect to a d line. In each ofthe following examples, surfaces marked with asterisks (*) areaspherical surfaces, and the shape of the aspherical surfaces is definedby the following equation:

$\begin{matrix}{X = {\frac{C_{j}h^{2}}{1 + \sqrt{1 - {( {1 + K_{j}} )C_{j}^{2}h^{2}}}} + {\sum{A_{j,n}h^{n}}}}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

where X is the distance from a point on an aspherical surface with aheight h from the optical axis to a tangential plane at the vertex ofthe aspherical surface, h is the height from the optical axis, Cj is thecurvature at the vertex of the j-th aspherical surface (Cj=1/Rj), Kj isthe conical constant of the j-th surface, and Aj,n is the n-th orderaspherical coefficient of the j-th surface.

Example 1

An illuminating lens of Example 1 has a shape corresponding to thatshown in FIG. 3. Example 1 is an example of an illuminating lensdesigned to widen the range of transmission directions for light from a0.5 mm cubic-shaped light emitting diode as a light source. Table 1shows the surface data of the illuminating lens of Example 1, and Table2 shows the aspherical surface data thereof.

TABLE 1 Surface data Surface number r d n Object surface ∞ 0.964 1.41 1*8.373E−13 7.036 Image surface ∞

TABLE 2 Aspherical surface data First surface K = −1.0268E+01, A3 =1.9628E+00, A4 = −8.3686E+00, A5 = 1.9670E+01 A6 = −3.6276E+01, A7 =4.6681E+01, A8 = −3.0918E+01, A9 = −1.0909E−01 A10 = 1.0608E+01, A11 =−7.0489E−03, A12 = −4.5201E+00, A13 = 1.2256E−02 A14 = 1.4688E+00, A15 =3.4825E−04, A16 = −3.1939E−01, A17 = −7.9209E−04 A18 = 4.0742E−02, A19 =3.5721E−05, A20 = −2.2613E−03

FIG. 8 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that the illuminating lensof Example 1 and the light emitting diode are used and the surface to beirradiated is placed at a distance of 8 mm from the light emittingsurface of the light emitting diode.

FIG. 9 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that only the same lightemitting diode is used and the surface to be irradiated is placed at adistance of 8 mm from the light emitting surface of the light emittingdiode.

A comparison between FIG. 8 and FIG. 9 shows that the illuminating lensof Example 1 is effective in increasing the illuminated area of thesurface to be irradiated.

FIG. 10 shows the curvature C of micro-segments of the illuminating lensof Example 1. The horizontal axis represents the angle θi between theoptical axis and the line Li connecting the center of each of themicro-segments and the position of the light source on the optical axis(see FIG. 4). The curvature C reverses its sign at 13.77 degrees, andhas a maximum value at 69.8 degrees.

FIG. 11 shows C×(n−1)×di related to the inequality (4) for theilluminating lens of Example 1, where di represents the distance fromthe position of the light source on the optical axis to the center ofeach of the micro-segments, that is, the length of the line Li in FIGS.4.

C×(n−1)×di has a maximum value when the angle θi is 69.8 degrees, andthe value is 1.51.

FIG. 12 shows the curvature C of micro-segments and the sag amount ofthe illuminating lens of Example 1. The angles θo, θs, and θmc are 13.77degrees, 37.06 degrees, and 69.8 degrees, respectively.

FIG. 13 shows a change in Δθr/Δθi with an increase in θi in theilluminating lens of Example 1. Δθr/Δθi changes in a waveform, and thedistance between the waves becomes narrower as θi increases.

FIG. 14 shows relative luminous intensities of light rays emitted fromthe light exit surface of the illuminating lens of Example 1, where thelight rays are sorted by respective emission angles. In FIG. 14, θmp is67.7 degrees. Therefore, θmp/θmc is 0.97.

Example 2

An illuminating lens of Example 2 has a shape corresponding to thatshown in FIG. 3. Example 2 is an example of an illuminating lensdesigned to widen the range of transmission directions for light from a0.65 mm cubic-shaped light emitting diode as a light source. Table 3shows the surface data of the illuminating lens of Example 2, and Table4 shows the aspherical surface data thereof.

TABLE 3 Surface data Surface number r d n Object surface ∞ 1.2 1.41 1*1.088E−12 6.8 Image surface ∞

TABLE 4 Aspherical surface data First surface K = −1.0268E+01, A3 =1.5843E+00, A4 = −5.9328E+00, A5 = 1.0800E+01 A6 = −1.3014E+01, A7 =1.0470E+01, A8 = −4.6299E+00, A9 = −2.1226E−02 A10 = 9.6894E−01, A11 =−7.9260E−02, A12 = −2.3661E−01, A13 = −1.8210E−03 A14 = 6.4025E−02, A15= 1.2197E−03, A16 = −1.0393E−02, A17 = −1.3892E−04 A18 = 8.1619E−05, A19= 6.2396E−04, A20 = −1.5184E−04

FIG. 15 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that the illuminating lensof Example 2 and the light emitting diode are used and the surface to beirradiated is placed at a distance of 8 mm from the light emittingsurface of the light emitting diode.

FIG. 16 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that only the same lightemitting diode is used and the surface to be irradiated is placed at adistance of 8 mm from the light emitting surface of the light emittingdiode.

A comparison between FIG. 15 and FIG. 16 shows that the illuminatinglens of Example 2 is effective in increasing the illuminated area of thesurface to be irradiated.

FIG. 17 shows the curvature C of micro-segments of the illuminating lensof Example 2. The horizontal axis represents the angle θi between theoptical axis and the line Li connecting the center of each of themicro-segments and the position of the light source on the optical axis.The curvature C reverses its sign at 12.5 degrees, and has a maximumvalue at 67.2 degrees.

FIG. 18 shows C×(n−1)×di related to the inequality (4) for theilluminating lens of Example 2. C×(n−1)×di has a maximum value when theangle θi is 67.2 degrees, and the value is 1.53.

FIG. 19 shows the curvature C and the sag amount of micro-segments ofthe illuminating lens of Example 2. The angles θo, θs, and θmc are 12.5degrees, 35.38 degrees, and 67.2 degrees, respectively. FIG. 20 shows achange in Δθr/Δθi with an increase in of in the illuminating lens ofExample 2. Δθr/Δθi changes in a waveform, and the distance between thewaves becomes narrower as θi increases.

FIG. 21 shows relative luminous intensities of light rays emitted fromthe light exit surface of the illuminating lens of Example 2, where thelight rays are sorted by respective emission angles. In FIG. 21, θmp is62.5 degrees. Therefore, θmp/θmc is 0.93.

Example 3

An illuminating lens of Example 3 has a shape corresponding to thatshown in FIG. 3. Example 3 is an example of an illuminating lensdesigned to widen the range of transmission directions for light from a0.95 mm cubic-shaped light emitting diode as a light source. Table 5shows the surface data of the illuminating lens of Example 3, and Table6 shows the aspherical surface data thereof.

TABLE 5 Surface data Surface number r d n Object surface ∞ 2.462 1.4921* 2.177E−12 13.538 Image surface ∞

TABLE 6 Aspherical surface data First surface K = −2.8085E+01, A3 =8.1962E−01, A4 = −1.3756E+00, A5 = 1.0351E+00 A6 = −4.6852E−01, A7 =1.5092E−01, A8 = −3.3498E−02, A9 = 6.6020E−04 A10 = 1.9319E−03, A11 =−1.0865E−04, A12 = −1.2491E−04, A13 = −1.2357E−06 A14 = 7.9995E−06, A15= 2.0909E−07, A16 = −3.0106E−07, A17 = −2.5477E−09 A18 = −6.1609E−10,A19 = 2.0427E−09, A20 = −2.1669E−10

FIG. 22 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that the illuminating lensof Example 3 and the light emitting diode are used and the surface to beirradiated is placed at a distance of 16 mm from the light emittingsurface of the light emitting diode.

FIG. 23 shows the illuminance distribution on the surface to beirradiated obtained by calculation assuming that only the same lightemitting diode is used and the surface to be irradiated is placed at adistance of 16 mm from the light emitting surface of the light emittingdiode.

A comparison between FIG. 22 and FIG. 23 shows that the illuminatinglens of Example 3 is effective in increasing the illuminated area of thesurface to be irradiated.

FIG. 24 shows the curvature C of micro-segments of the illuminating lensof Example 3. The horizontal axis represents the angle θi between theoptical axis and the line Li connecting the center of each of themicro-segments and the position of the light source on the optical axis.The curvature C reverses its sign at 13.56 degrees, and has a maximumvalue at 69.52 degrees.

FIG. 25 shows C×(n−1)×di related to the inequality (4) for theilluminating lens of Example 3. C×(n−1)×di has a maximum value when theangle θi is 69.52 degrees, and the value is 1.47.

FIG. 26 shows the curvature C and the sag amount of micro-segments ofthe illuminating lens of Example 3. The angles θo, θs, and θmc are 13.56degrees, 35.66 degrees, and 69.52 degrees, respectively.

FIG. 27 shows a change in Δθr/Δθi with an increase in θi in theilluminating lens of Example 3. Δθr/Δθi changes in a waveform, and thedistance between the waves becomes narrower as θi increases.

FIG. 28 shows relative luminous intensities of light rays emitted fromthe light exit surface of the illuminating lens of Example 3, where thelight rays are sorted by respective emission angles. In FIG. 28, θmp is69.52 degrees. Therefore, θmp/θmc is 1.00.

Table 7 below shows the values corresponding to the conditions definedby the inequalities (1) to (9) for the illuminating lenses of Examples 1to 3.

TABLE 7 Values corresponding to conditions θmp/ Cm × θi in Yr in θmc in(n − 1) × d θo in inequality inequality inequality in inequalityinequality (1) (2) (3) (4) (5) Example 1 69.8 0.93 0.97 1.51 13.77Example 2 67.2 0.94 0.93 1.53 12.50 Example 3 69.5 0.96 1.00 1.47 13.56θs in n in D/t in D/De in inequality inequality inequality inequality(6) in (7) (8) (9) Example 1 37.06 1.410 0.519 0.11 Example 2 35.381.410 0.541 0.17 Example 3 35.66 1.492 0.386 0.10

Third Embodiment

FIG. 29 is a schematic diagram of a surface light source 800 accordingto a third embodiment of the present invention. This surface lightsource 800 includes the plurality of lighting devices 700 described inthe second embodiment arranged in a plane, and a diffusing plate 400disposed to cover the plurality of lighting devices 700. The lightingdevices 700 may be arranged in a matrix as shown in FIG. 29. They may bearranged in a staggered manner as shown in FIG. 31.

The surface light source 800 includes a substrate 650 facing thediffusing plate 400 with the lighting devices 7 being disposedtherebetween. As shown in FIG. 30, the light emitting diode 200 of eachlighting device 700 is mounted on the substrate 650. In the presentembodiment, a reflecting plate 600 is disposed on the substrate 650 tocover the substrate 650 with the light emitting diodes 200 beingexposed. In the present embodiment, the light entrance surface 111 ofthe illuminating lens 100 and the bottom surface 112 surrounding thelight entrance surface 111 are on the same level.

The lighting device 700 emits light to one surface (light entrancesurface) of the diffusing plate 400. That is, the one surface of thediffusing plate 400 is the surface to be irradiated 300 that has beendescribed in the first and second embodiments. The diffusing plate 400emits the light received on its one surface from the other surface(light exit surface) in a diffused manner. The lighting devices 700 emitlight individually toward a large area of the one surface of thediffusing plate 400 so that the one surface has a uniform illuminance,and upon receiving this light, the diffusing plate 400 emits the lightdiffusely. As a result, the surface light source capable of emittinglight having less uneven brightness in the plane is obtained.

The light emitted from the lighting device 700 is diffused by thediffusing plate 400 so that the diffuse light returns to the lightingdevice side or passes through the diffusing plate 400. The light thathas returned to the lighting device side and struck the reflecting plate600 is reflected at the reflecting plate 600 and again enters thediffusing plate 400.

It is preferable that the surface light source 800 satisfies thefollowing inequality (10):

0.2<h/p<0.4  (10)

(more preferably, 0.25<h/p<0.35  (10)′)

where h is the distance from the light emitting surface of the lightemitting diode 200 in each of the lighting devices 700 to the lightentrance surface of the diffusing plate 400, and p is the arrangementpitch of the lighting devices 700.

The inequality (10) (or the inequality (10)′) defines the distancebetween the light emitting surface of each of the lighting devices 700and the diffusing plate 400 with respect to the arrangement pitch of thelighting devices 700. As stated herein, the “arrangement pitch” meansthe distance between the optical axes of the adjacent lighting devices700 in the direction in which the lighting devices 700 are aligned.There are two orthogonal directions of alignment of the lighting devices700, that is, lateral and longitudinal directions thereof in the casewhere they are arranged in a matrix as shown in FIG. 29. There are twodirections, that is, lateral and oblique directions in the case wherethey are arranged in a staggered manner as shown in FIG. 31. The pitchin one direction need not necessarily coincide with that in the otherdirection, but preferably, the pitches in these two directions coincidewith each other.

If the value of h/p exceeds the upper limit of the inequality (10) (orthe inequality (10)′), the diffusing plate 400 is too far from thelighting devices 700 with respect to the arrangement pitch of thelighting devices 700, which increases the surface light source in size.If the value of h/p is less than the lower limit, it is difficult tomaintain the uniformity in the brightness distribution on the diffusingplate 400, which increases the unevenness of in-plane brightness.

Furthermore, it is preferable that the surface light source 800satisfies the following inequality (11):

0.04<D/h<0.15  (11)

(more preferably, 0.05<D/h<0.13  (11)′)

where D is the maximum width of the light emitting surface of the lightemitting diode 200, and h is the distance from the light emittingsurface of the light emitting diode 200 in each of the lighting devices700 to the light entrance surface of the diffusing plate 400.

The inequality (11) (or the inequality (11)′) defines the size of thelight emitting diode 200 with respect to the distance between the lightemitting surface of each of the lighting devices 700 and the diffusingplate 400. If the value of D/h exceeds the upper limit of the inequality(11) (or the inequality (11)′), the size of the light emitting diode 200is excessively large with respect to the distance between the lightemitting surface of each of the lighting devices 700 and the diffusingplate 400. As a result, it is difficult to ensure the lens powerrequired to widen the range of light distribution by using theilluminating lens 100. If the value of D/h is less than the lower limit,the distance between the light emitting surface of each of the lightingdevices 700 and the diffusing plate 400 is excessively large withrespect to the size of the light emitting diode 200, which increases thesurface light source in size.

Table 8 below shows the values corresponding to the conditions definedby the inequalities (10) and (11), which are obtained by using Examples1 to 3 shown in the second embodiment.

TABLE 8 Values corresponding to conditions h/p in D/h in inequalityinequality (10) (11) Example 1 0.29 0.063 Example 2 0.29 0.081 Example 30.29 0.059

Fourth Embodiment

FIG. 32 is a schematic diagram of a liquid-crystal display apparatusaccording to a fourth embodiment of the present invention. Thisliquid-crystal display apparatus includes a liquid-crystal panel 500,and a surface light source 800 described in the third embodimentdisposed behind the liquid-crystal panel 500.

A plurality of lighting devices 700 each including the light emittingdiode 200 and the illuminating lens 100 are arranged in a plane, and thediffusing plate 400 is illuminated by these lighting devices 700. Theunderside (one surface) of the diffusing plate 400 is irradiated withthe light emitted from the lighting devices 700 to have a uniformilluminance, and then the light is diffused by the diffusing plate 400.Thus, the liquid-crystal panel 500 is illuminated by the diffused light.

It is preferable that an optical sheet such as a diffusing sheet or aprism sheet is disposed between the liquid-crystal panel 500 and thesurface light source 800. In this case, the light that has passedthrough the diffusing plate 400 further is diffused by the optical sheetand illuminates the liquid-crystal panel 500.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this specification are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1-17. (canceled)
 18. An illuminating lens for spreading light emittedfrom a light source so that a surface to be irradiated is irradiatedwith the spread light, the lens comprising: a light entrance surfacethrough which the light emitted from the light source enters the lens;and a light exit surface through which the light that has entered thelens exits the lens, the light exit surface being rotationally symmetricwith respect to an optical axis, wherein the light exit surface has aconcave portion and a convex portion, the concave portion intersectingthe optical axis, and the convex portion being provided around theconcave portion to extend continuously from the concave portion, thelight exit surface is formed in a shape such that when the light exitsurface is divided into micro-segments in a cross section that includesthe optical axis, wherein the micro-segments have respective curvaturesC, a maximum curvature Cm among curvatures C is positioned outward froma midpoint of the convex portion, and a position of a micro-segment withthe maximum curvature Cm is within a range defined by the followinginequality (1):60°<θi<80°  (1) where θi is an angle between the optical axis and a lineconnecting a position of the light source on the optical axis and acenter of each of the micro-segments.
 19. A lighting device comprising:a light emitting diode for emitting light; and the illuminating lensaccording to claim 18 for spreading light emitted from the lightemitting diode so that a surface to be irradiated is irradiated with thespread light.
 20. The lighting device according to claim 19, satisfyingthe following inequality (8):0.3<D/t<0.9  (8) where D is a maximum width of a light emitting surfaceof the light emitting diode, and t is a center thickness of theilluminating lens.
 21. The lighting device according to claim 19,satisfying the following inequality (9):0.06<D/De<0.27  (9) where D is a maximum width of a light emittingsurface of the light emitting diode, and De is an effective diameter ofthe illuminating lens.
 22. An illuminating lens for spreading lightemitted from a light source so that a surface to be irradiated isirradiated with the spread light, the lens comprising: a light entrancesurface through which the light emitted from the light source enters thelens; and a light exit surface through which the light that has enteredthe lens exits the lens, the light exit surface being rotationallysymmetric with respect to an optical axis, wherein the light exitsurface has a concave portion and a convex portion, the concave portionintersecting the optical axis, and the convex portion being providedaround the concave portion to extend continuously from the concaveportion, the light exit surface is formed in a shape such that when thelight exit surface is divided into micro-segments in a cross sectionthat includes the optical axis, wherein the micro-segments haverespective curvatures C, a maximum curvature Cm among curvatures C ispositioned outward from a midpoint of the convex portion, and a positionof a micro-segment with the maximum curvature Cm is within a rangedefined by the following inequality (2):0.88<Yr<0.98  (2) where Yr is a ratio of a distance from the opticalaxis to a center of each of the micro-segments with respect to half aneffective diameter of the illuminating lens.
 23. A lighting devicecomprising: a light emitting diode for emitting light; and theilluminating lens according to claim 22 for spreading light emitted fromthe light emitting diode so that a surface to be irradiated isirradiated with the spread light.
 24. The lighting device according toclaim 23, satisfying the following inequality (8):0.3<D/t<0.9  (8) where D is a maximum width of a light emitting surfaceof the light emitting diode, and t is a center thickness of theilluminating lens.
 25. The lighting device according to claim 23,satisfying the following inequality (9):0.06<D/De<0.27  (9) where D is a maximum width of a light emittingsurface of the light emitting diode, and De is an effective diameter ofthe illuminating lens.
 26. An illuminating lens for spreading lightemitted from a light source so that a surface to be irradiated isirradiated with the spread light, the lens comprising: a light entrancesurface through which the light emitted from the light source enters thelens; and a light exit surface through which the light that has enteredthe lens exits the lens, the light exit surface being rotationallysymmetric with respect to an optical axis, wherein the light exitsurface has a concave portion and a convex portion, the concave portionintersecting the optical axis, and the convex portion being providedaround the concave portion to extend continuously from the concaveportion, the light exit surface is formed in a shape such that when thelight exit surface is divided into micro-segments in a cross sectionthat includes the optical axis, wherein the micro-segments haverespective curvatures C, a maximum curvature Cm among curvatures C ispositioned outward from a midpoint of the convex portion, and the lightexit surface satisfies the following inequality (3):0.90<θmp/θmc<1.05  (3) where θmc is an angle between the optical axisand a line connecting a position of the light source on the optical axisand a center of a micro-segment with the maximum curvature Cm, and θmpis, among emission angles that are angles between light rays emittedfrom the light exit surface and the optical axis, an emission anglehaving a maximum luminous intensity, where the light rays are sorted byrespective emission angles.
 27. A lighting device comprising: a lightemitting diode for emitting light; and the illuminating lens accordingto claim 26 for spreading light emitted from the light emitting diode sothat a surface to be irradiated is irradiated with the spread light. 28.The lighting device according to claim 27, satisfying the followinginequality (8):0.3<D/t<0.9  (8) where D is a maximum width of a light emitting surfaceof the light emitting diode, and t is a center thickness of theilluminating lens.
 29. The lighting device according to claim 27,satisfying the following inequality (9):0.06<D/De<0.27  (9) where D is a maximum width of a light emittingsurface of the light emitting diode, and De is an effective diameter ofthe illuminating lens.